1. Field of the Invention
This invention relates to apparatus for superimposition of television images and, more specifically, such apparatus which is adapted to provide stable superimposition to produce an improved representation of superimposed live television and recorded images.
2. Description of the Prior Art
Various systems for employing electronic processing of image data have been known. See, for example, U.S. Pat. Nos. 3,961,133 and 4,011,401.
It has also been known that a recorded image may advantageously be combined with a real-time or live television image in order to provide for more efficient use of image data. In many uses of such systems, there is a great need for high quality equipment so as to provide images devoid of distortion or misrepresentation of the spatial information. For example, in the medical environment, it has been known to employ a subtraction concept to provide an image of enhanced quality through deletion of bones or other fixed objects from the final image. It has also been known to employ superimposition as a means for more effective catheterization techniques. In such use, an image of a blood vessel with its branches may be superimposed upon an image of a catheter. Such uses are disclosed in an article entitled "Electronic Radiography in Stereotaxic Thrombosis of Intracranial Aneurysms and Catheter Embolization of Cerebral Arteriovenous Malformations" which appears at pages 359-363 in Volume 105, No. 2 issue of Radiology, (Nov. 1972).
One of the problems encountered with such systems for coordinating the superimposition of a live television image with previously recorded video disc information has been the need for a very highly stabilized magnetic disc recorder including feedback circuits. Such a system requires a very costly and complex disc system which is relatively expensive to maintain, is heavy and provides, in spite of precautions, inherent instability that results in some degree of undesired misregistration (such as 200-400 nanosecond jitter, for example). The discs employed in such systems inherently result in some degree of localized variation in disc velocity. By contrast, in such a system, the video signal which is generated by a television camera is generally rather stable (such as 10-50 nanosecond jitter, for example).
There remains, therefore, a specific need for apparatus which may economically and more effectively provide for superimposition of recorded images with television images in a fashion which reduces the misregistration on the displayed or recorded image.